Enhanced Superconducting Properties Research Articles

Advancing processing of the ternary (Sm,Eu,Gd)Ba2Cu3O7-y superconductor via top-seeded infiltration growth

In this study, we present the fabrication of large single-domain ternary (Sm,Eu,Gd)Ba2Cu3O7-y bulk superconductor with enhanced superconducting properties using various REBa2Cu3Oy (RE-123) as a liquid source via the top-seeded infiltration growth process (TSIG) in air. We employed a 1:1 ratio of REBa2Cu3Oy (RE = Sm, Gd, Y and Er) and Ba3Cu5O8 as a liquid source for fabrication. Impressively, all the obtained bulk samples exhibited a superconducting transition temperature T(c, onset) above 94 K. However, the bulk sample fabricated using Y-123 + Ba3Cu5O8 as a liquid source demonstrated a T(c, onset) of 94.53 K, with a 40.14 % improvement in transition width (ΔTc) and at 77 K the bulk recorded a self-field critical current density (Jc) value of 44.73 kA/cm2 & 10.62 kA/cm2 at 1T resulting in a remarkable 93.08 % improvement in self-field Jc compared to the bulk sample fabricated using Er-123 + Ba3Cu5O8. Microstructural analysis using a scanning electron microscope revealed a significant reduction in the mean size of secondary (211) phase particles, a significant reduction of 38.41 % is observed for the Y-123 + Ba3Cu5O8 employed sample.

First-principles study of superconducting transition temperature of niobium and vanadium as a function of pressure

Ultra-high pressure has recently led to the observation of high Tc superconductors. The exploration of superconducting properties under high pressure conditions offers valuable insights into the fundamental mechanisms governing superconductivity and opens avenues for the synthesis of novel materials with enhanced superconducting properties. In this study, the superconducting transition temperature, Tc, for niobium and vanadium has been investigated to maximum pressures of 250.0 and 70.0 GPa, respectively. Density functional theory and density functional perturbation theory were used to undertake first-principles computations to investigate the variations of superconducting properties under pressure. For both the metals niobium (Nb) and vanadium (V), we observed that the density of states at the Fermi level decreased, while the overall phonon frequency generally increased with pressure. For Nb, we find that the electron–phonon coupling constant (λ) and the superconducting transition temperature (Tc) decrease steadily with pressure; however, for V, we find that λ and Tc decrease smoothly up to 26.0 GPa, and then gradually increase to 70.0 GPa pressure. The observed phonon spectrum nature for both Nb and V is in good agreement with the neutron scattering approach’s output.

Growth of Bi2Sr2CaCu2O8+δ thin films with enhanced superconducting properties by incorporating NiO nanoparticles

A series of Bi2Sr2CaCu2O8+δ–xNiO (x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) thin films were prepared by Pechini sol-gel method. With the doping of NiO, the microstructure and superconducting properties of thin films samples were characterized and analyzed particularly. All main peaks in XRD patterns corresponded to the (00l) diffraction peaks of Bi2212, demonstrating an excellent c-axis epitaxial growth of thin films samples. The second phase primarily existed in the form of highly textured with (200) epitaxy NiO crystal. Meanwhile, it was found that both Bi2212 matrix and NiO phase are characteristic of in-plane four-axis symmetry and the in-plane orientation relationship among the NiO phase, the Bi2212 matrix and the STO substrate can be determined to be Bi2212[100](001)//NiO[011](100)//STO[011](100). The effects of the doped NiO on the anisotropy of Bi2212 crystal growth is not significant. In addition, it was concluded that the zero resistivity superconducting transition temperature (Tc, zero) was decreasing with increasing doping level x, as well as thin films sample N2 (x = 0.2) exhibited the best current carrying capacity in magnetic field.

Enhanced superconducting properties of double-chain based superconductor Pr[formula omitted]Ba[formula omitted]Cu[formula omitted]O[formula omitted] synthesized by citrate pyrolysis technique

We report the enhanced superconducting properties of double-chain based superconductor Pr2Ba4Cu7O15−δ synthesized by the citrate pyrolysis technique. The reduction heat treatment in vacuum results in the appearance of superconducting state with Tc=22-24 K, accompanied by the higher residual resistivity ratios. The superconducting volume fractions are estimated from the ZFC data to be 50∼55%, indicating the bulk superconductivity. We evaluate from the magneto-transport data the temperature dependence of the superconducting critical field, to establish the superconducting phase diagram. The upper critical magnetic field is estimated to be about 35 T at low temperatures from the resistive transition data using the Werthamer-Helfand-Hohenberg formula. The Hall coefficient RH of the 48-h-reduced superconducting sample is determined to be −0.5×10−3cm3/C at 30 K, suggesting higher electron concentration. These findings have a close relationship with homogeneous distributions of the superconducting grains and improved weak links between their superconducting grains in the present synthesis process.

Ultrafast transient liquid assisted growth of high current density superconducting films

The achievement of high growth rates in YBa2Cu3O7 epitaxial high-temperature superconducting films has become strategic to enable high-throughput manufacturing of long length coated conductors for energy and large magnet applications. We report on a transient liquid assisted growth process capable of achieving ultrafast growth rates (100 nm s−1) and high critical current densities (5 MA cm−2 at 77 K). This is based on the kinetic preference of Ba-Cu-O to form transient liquids prior to crystalline thermodynamic equilibrium phases, and as such is a non-equilibrium approach. The transient liquid-assisted growth process is combined with chemical solution deposition, proposing a scalable method for superconducting tapes manufacturing. Additionally, using colloidal solutions, the growth process is extended towards fabrication of nanocomposite films for enhanced superconducting properties at high magnetic fields. Fast acquisition in situ synchrotron X-ray diffraction and high resolution scanning transmission electron microscopy (STEM) become crucial measurements in disentangling key aspects of the growth process.

Reliable single grain growth of (RE)BCO bulk superconductors with enhanced superconducting properties

We review recent progress in the successful and reliable fabrication of large grain (RE)BCO and (RE)BCO–Ag bulk high temperature superconductors by three primary processing methodologies: top-seeded melt growth (TSMG), top-seeded infiltration growth (TSIG) and a combined processing route comprising both TSMG and TSIG. Several significant and useful modifications have been made to these processing routes over the recent years in order to grow (RE)BCO single grains reliably and to enhance their superconducting properties. With respect to the reliable growth of (RE)BCO single grains, we have further developed the so-called buffer technique for reliable seeding, which includes identifying and providing an appropriate liquid-rich phase at the bottom of pellet. This modification has proved to be critical to the success of the newly-developed fabrication techniques presented here. In addition, we have addressed existing and significant challenges in the context of improving the superconducting properties of the bulk samples by controlling the microstructures of single grain materials (porosity and the RE-211 distribution, in particular) and by suppressing the extent of RE/Ba substitution during grain growth. Finally, we provide a short summary of the potential pathways towards realising practical applications of these technologically important materials in the near future.

Superconductivity in REO0.5F0.5BiS2 with high-entropy-alloy-type blocking layers

We synthesized new REO0.5F0.5BiS2 (RE: rare earth) superconductors with high-entropy-alloy-type (HEA-type) REO blocking layers. The lattice constant a systematically changed in the HEA-type samples with the RE concentration and the RE ionic radius. A sharp superconducting transition was observed in the resistivity measurements for all the HEA-type samples, and the transition temperature of the HEA-type samples was higher than that of typical REO0.5F0.5BiS2. The sharp superconducting transition and the enhanced superconducting properties of the HEA-type samples may indicate the effectiveness of the HEA states of the REO blocking layers in the REO0.5F0.5BiS2 system.

Effect of ZnO/TiO2 Nanorods Fabricated Using the Electrospinning Method in Y-Ba-Cu-O Single Grain Bulk Superconductors

In this study, the enhanced superconducting properties of single grain bulk Y-Ba-Cu-O (YBCO) superconductors by the addition of ZnO and TiO 2 nano-rods (NRs) were investigated. The NRs were prepared using the electrospinning method, in which size is twice the coherence length of the superconductor and is intended supposed to serve as columnar defects to provide efficient pinning. The experimental results showed that there were no weak links formed by the addition of the NRs. All of the bulks exhibited a single grain structure, and the distribution profiles of the trapped fields were symmetrical. The value of the maximum trapped field (Bt, max) was enhanced to 0.12 T, which was 1.5 times higher than the undoped sample (approximately 0.08 T). In addition, JJ was also enhanced by the addition of the NRs. The self-field at 77 K was 4.6 χ 10 4 A cm -2 of the 0.05wt% ZnO NRsdoped and 0.1wt% TiO 2 NRs-doped samples, respectively, which was higher than that of the undoped sample of 2.5 χ 10 4 A cm -2 . A microstructural analysis demonstrated that there was no reaction occurred between the NRs and YBCO precursors during the melting process. The size and shape of the NRs found in the matrix of the grown bulk were the same as those of the precursors. Consequently, the enhanced superconductivities were then attributed to the increased interface areas between the NRs and the matrix.

ChemInform Abstract: The Intercalation Chemistry of Layered Iron Chalcogenide Superconductors

AbstractReview: 158 refs.

The intercalation chemistry of layered iron chalcogenide superconductors

The iron chalcogenides FeSe and FeS are superconductors composed of two-dimensional sheets held together by van der Waals interactions, which makes them prime candidates for the intercalation of various guest species. We review the intercalation chemistry of FeSe and FeS superconductors and discuss their synthesis, structure, and physical properties. Before we review the latest work in this area, we provide a brief background on the intercalation chemistry of other inorganic materials that exhibit enhanced superconducting properties upon intercalation, which include the transition metal dichalcogenides, fullerenes, and layered cobalt oxides. From past studies of these intercalated superconductors, we discuss the role of the intercalates in terms of charge doping, structural distortions, and Fermi surface reconstruction. We also briefly review the physical and chemical properties of the host materials—mackinawite-type FeS and β-FeSe. The three types of intercalates for the iron chalcogenides can be placed in three categories: 1.) alkali and alkaline earth cations intercalated through the liquid ammonia technique; 2.) cations intercalated with organic amines such as ethylenediamine; and 3.) layered hydroxides intercalated during hydrothermal conditions. A recurring theme in these studies is the role of the intercalated guest in electron doping the chalcogenide host and in enhancing the two-dimensionality of the electronic structure by spacing the FeSe layers apart. We end this review discussing possible new avenues in the intercalation chemistry of transition metal monochalcogenides, and the promise of these materials as a unique set of new inorganic two-dimensional systems.

Analysis of Internally Shunted Josephson Junctions

Following the ever-rising demand for new functionalities and novel materials in superconducting circuitry, we provide a complete view on the self-shunting problem in Josephson junctions, relating it to specific features of a multichannel weak link between electrodes where averaging over the channels yields a bimodal distribution of transparencies with maxima near unity and zero. We provide two examples of such internally shunted devices, namely, four-layered Nb/Al-Al oxide-Nb junctions with strongly disordered nanometer-thick insulating layers where stochastic distribution of transparencies takes place on a local rather than a global scale and MoRe/W-doped Si-Si-MoRe devices with strongly inhomogeneous silicon interlayers partly doped by metallic nanoclusters where the main charge transport occurs across resonance-percolating trajectories. We show how the predicted universal distribution function of transmission coefficients can be verified experimentally without any fitting parameters and analyze some old and new experimental data from this perspective. We believe that our results can form a base for novel four-layered Josephson junctions with enhanced superconducting properties and, at the same time, well-separated metallic electrodes.

Nanostructured pinning centers in FeSe0.1Te0.9 thin films for enhanced superconducting properties

FeSe0.1Te0.9 thin films were deposited on single crystal SrTiO3 (STO) (100) substrates by a pulse laser deposition (PLD) technique. CeO2 nanolayer was introduced as either cap layer or buffer layer to investigate its pinning effects in FeSe0.1Te0.9 thin films. The results show improved film quality after doping with CeO2 nanolayers, and no impurity phase was identified. All the samples achieve Tc of 12.5 K, and in-field Jc was greatly enhanced after doping with either cap or buffer CeO2 nanolayer for the field range up to 7 T. The buffered one shows the best self-field Jc of 0.89 MA cm−2 at 4 K and a high upper critical field Hc2 of 186 T.

Growth of Bi2Sr2CaCu2O8+δ thin films with enhanced superconducting properties by incorporating CaIrO3 nanoparticles

We synthesized Bi2Sr2CaCu2O8+δ (Bi-2212) thin films with incorporated CaIrO3 (Ca-iridate) nanoparticles, by using pulsed laser deposition and post-growth ex situ annealing. We found that the density of incorporated Ca-iridate strongly affected the superconducting properties and microstructure of the Bi-2212 thin films. Incorporating a low density of Ca-iridate (450 laser pulses) in the Bi-2212 improved its superconducting properties (Tc-onset = 97 K, Tc-zero = 84 K) over those of pure Bi-2212 (Tc-onset = 94 K, Tc-zero = 80 K). However, incorporating a higher density (1800 pulses) significantly reduced Tc-zero to ≈ 57 K. Incorporating a low density of Ca-iridate also decreased the c-axis lattice constant. Films with incorporated Ca-iridate exhibited greater critical current density, Jc(B), than the pure Bi-2212 film. These results indicate that incorporating low densities of Ca-iridate nanoparticles into Bi-2212 can improve its superconducting properties.

Evidence for multiple superconducting gaps in the filled skutterudite compound LaRu4As12

Superconducting properties of the filled skutterudite compound LaRu${}_{4}$As${}_{12}$ were investigated both as a function of temperature and magnetic field. At $T\ensuremath{\ll}{T}_{\mathrm{c}}=10.45$ K, the electronic contribution to the specific heat was found to be at variance with the predictions for an $s$-wave superconductor with one energy gap. In constant applied fields up to ${H}_{\mathrm{c}2}(0)\ensuremath{\approx}10.2$ T, multiple gaps have been further inferred from both a nonlinear magnetic-field dependence of the specific heat in the zero-temperature limit and a positive curvature of the upper critical field in the vicinity of ${T}_{\mathrm{c}}$. Thus, LaRu${}_{4}$As${}_{12}$ appears to be a rare multiple-gap superconductor with cubic symmetry. Intriguing evidence for multiband effects is observed in the compound with enhanced superconducting properties as compared to other skutterudite superconductors.

Fe–Te–Se epitaxial thin films with enhanced superconducting properties

Epitaxial Fe–Te–Se thin films were deposited by pulsed laser deposition at 250–600 °C on SrTiO3 (100), MgO (100), LaAlO3 (100) and CaF2 (100) single crystal substrates. The best superconducting film was grown on CaF2: K and K with Tdep = 300 °C and 3 Hz. Critical current density Jc (T = 4.2 K) was 0.41 × 106 A cm−2 at 0 T and 0.23 × 106 A cm−2 at 9 T. The angular dependence of Jc shows a broad c-axis correlated peak when B ≥ 3 T.

Comparison of the superconducting properties of Cu0.5Tl0.5Ba2Ca2(Cu3−yZny)O10−δ prepared at different synthesis temperatures

The superconducting properties of Zn-doped Cu0.5Tl0.5Ba2Ca2(Cu3−yZny)O10−δ {CuTlZn-1223} (y=0, 0.83, 1.66, 2.5) samples prepared at 820, 830, 850 and 860°C have been compared. The samples were investigated by x-ray diffraction (XRD), dc-resistivity, ac-susceptibility and Fourier Transform Infrared (FTIR) absorption measurements. Almost all the superconducting properties have been increased to their maximum in all CuTlZn-1223 samples synthesized at 860°C, which shows that 860°C is the optimum temperature to achieve CuTlZn-1223 with enhanced superconducting properties.

Influence of Ce Substitution at Sr-Site on Superconducting Fluctuation Behavior and Infrared Absorption of Tl0.9Bi0.1Sr2−x Ce x Ca0.9Y0.1Cu1.99Fe0.01O7−δ (x=0–0.20) Ceramics

Ce substituted Tl0.9Bi0.1Sr2−xCexCa0.9Y0.1Cu1.99Fe0.01O7−δ (x=0–0.20) samples were synthesized to determine the effects of the higher valence ion substitution on superconductivity and structure of the Fe-doped Tl1212 derivatives. The normal state behavior for x=0 showed semiconductor-like behavior which gradually turned to metallic behavior with increasing Ce at x=0.05–0.15. However, further substitution of Ce for x>0.15 turned the normal state to insulating behavior. The zero critical temperature, Tc zero increased from 65.4 K (x=0.05) to 71.0 K (x=0.10), but slightly decreased for x>0.10 indicating the optimum value of average copper valence was achieved at x=0.10. Excess conductivity analysis using the Aslamazov Larkin, AL and Lawrence–Doniach, LD models revealed two-dimensional, 2D to three-dimensional, 3D transition of superconducting fluctuation behavior, SFB with the highest transition temperature, \(T_{\mathrm{2D}\mbox{-}\mathrm{3D}}\) at x=0.10. FTIR analysis in conjunction with XRD results showed softening of FeO2/CuO2 planar oxygen mode from 610.5 cm−1(x=0) to 605 cm−1(x=0.20) which is suggested to be related to possible increase of inter plane coupling, J and this is supported by computed results based on the LD model. The enhanced J increases superconducting coherence length along c-axis, ξc(0), and hence lowers anisotropy, γ resulting in enhanced superconducting properties.

Nanostructured epitaxial thin films of Fe-based superconductors with enhanced superconducting properties

ABSTRACTEpitaxial Fe-Te-Se thin films were deposited by pulsed laser deposition at 250 ~ 600 °C on SrTiO3 (100, STO), MgO (100), LaAlO3 (100, LAO) and CaF2 (100) single crystal substrates. Best superconducting film was grown on CaF2: Tconset = 20.0 K and Tc0 = 16.18 K with Tdep = 300 °C, 45000 pulses, 3 Hz. The critical current density Jc at 4.2 K was 0.41×106A/cm2 at 0 T and 0.23×106 A/cm2 at 9 T. Angular dependence of Jc showed broad c-axis correlated peak when B ≥ 3 T.

Enhanced superconducting properties in epitaxial FeSe thin films with self-assembled Fe 3O 4 nanoparticles

In this paper we report epitaxial tetragonal iron selenide thin films grown on single crystal SrTiO 3 (STO) (0 0 1) and MgO (0 0 1) substrates by a pulsed laser deposition (PLD) technique. Deposition temperature and annealing process are found to be critical for achieving the tetragonal phase and the optimum superconducting properties of the films. The critical transition temperature of the thin films ranges from 2 K to 11.5 K depending on the deposition temperature and annealing condition. The samples with higher critical transition temperatures show better film crystallinity along with self-assembled Fe 3O 4 nanoparticles (∼15 nm in average particle size) in the films according to both X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. Besides the better crystallinity achieved in the films, the formation of Fe 3O 4 nanoparticles could assist the formation of the tetragonal FeSe phase and thus lead to the enhanced superconducting properties.

Pulsed laser deposition and in-field characterization of FeTe0.8S0.2 epitaxial thin films with enhanced superconducting properties

Fe–Te–S thin films deposited by pulsed laser deposition at 400°C on SrTiO3 (100) and MgO (100) single crystals showed epitaxy and 4-fold symmetry. Films deposited on both substrates reached zero resistance condition (Tc0=3.54K on STO and 5.37K on MgO) and presented large upper critical field (Bc2(0) = 61.1T on STO and 74.2T for MgO using 90% of the normal state resistance and Werthamer–Helfand–Hohenberg model), indicating that the coherence length ξ0 of the present films is very short (ξ0=2.3nm on STO and 2.1nm on MgO).